Conventionally, as disclosed in JP 2002-530245 A (corresponding to U.S. Pat. No. 6,941,194 B1), a communication system for a vehicle for exchanging a vehicle related data within the vehicle is well known. The communication system includes at least one calculate unit being placed in the vehicle for controlling a predetermined operation, which is also referred to as an application, a plurality of data sources coupled to the calculate unit, and an operation unit. The calculate unit includes a priority manage portion, which determines a priority of an access privilege to a data bus based on a present load state of the data bus.
Recently, a vehicle is usually equipped with more than one in-vehicle local area networks (LANs), and electronic control units. (ECU) equipped to the vehicle may be coupled to different LANs from one another. An ECU, which performs a predetermined operation, is also referred to as an application. In a case where ECUs coupled to the different LANs need to use a vehicle related data, which is transmitted from the same data source, an in-vehicle gateway apparatus may be disposed between the data source and the different LANs to which the ECUs are respectively coupled. The in-vehicle gateway apparatus receives the vehicle related data from the data source, converts the vehicle related data based on a corresponding protocol of each of the LANs. Then, the in-vehicle gateway apparatus transmits each converted vehicle related data to a corresponding LAN.
In the communication system disclosed in JP 2002-530245 A, when the in-vehicle gateway apparatus converts the vehicle related data based on the corresponding protocol of each of the LANs and transmits the converted data to the corresponding LAN, a communication traffic of a LAN having a low speed is more likely to increase than a communication traffic of a LAN having a high speed. Further a time when each ECU receives the vehicle related data, which is transmitted from the data source, may be different depending on the in-vehicle LAN coupled to each ECU. In this case, in order to perform a cooperative operation among the ECUs respectively coupled to the different LANs, one or more ECUs need to perform a data buffering in order to synchronize with other ECUs coupled to a different LAN. In this case, the ECUs are required to perform additional operations to achieve a synchronization compared with a case in which the data sources and the ECUs are coupled in a point-to-point manner.